what oil are you using?
how many miles do you put on in 3 weeks?
how much do you put in?
try switching to Rotella T6, get a compression check, could be a bad piston, turbo seal, or head gasket if you are losing coolant. or just bring it in for someone to take a look to get a definite answer

and search, its been covered and telling us it uses oil doesnt help cause there multiple problems that can be wrong with it

i put in 975 miles in 3 weeks and i use penzoil. high end oil.. and im not losing any coolant.